1. Field of the Invention
The present invention relates to the improvements of a blood pressure measuring apparatus which measures a blood pressure value of a living subject such as a patient.
2. Related Art Statement
There is known an automatic blood pressure (BP) measuring apparatus which carries out BP measurements on a patient, accumulatively stores a measured BP value or values obtained in each BP measurement, and provides a graphic representation of the stored BP values arranged in the order of measurement. An example of the BP measuring apparatus is disclosed in Non-Examined Japanese Patent Application laid open under Publication No. 5(1993)-137698. The BP apparatus enables the patient to easily recognize the time change of the measured BP values and correctly judge whether he or she is in a healthy condition. When the patient feels tight in the chest, such a light attack may, however, be transient, so that the patient may fail to recognize that he or she possibly has a serious heart disease. Even if the patient may reach the recognition and consult a doctor, then the patient may no longer have any subjective symptom and may appear to the doctor to have no medical problem. In this case, the doctor may make a diagnosis based on insufficient examination data, e.g., BP values only. If the prior BP apparatus is used to obtain the BP values of the patient, however, the BP apparatus provides only the measured BP values of the patient, or only the time change of the measured BP values. With those data, the patient may suspect that he or she may have hypertension, but the patient cannot make a self-diagnosis, or the doctor cannot make a medical diagnosis, that he or she may have a heart disease. If the patient continues his or her life without receiving any medical treatments, he or she might be brought into a serious condition.
There is also known an automatic BP measuring apparatus which has a BP measuring device for automatically measuring a BP value or values of a living body, and a BP-value storing device for accumulatively storing the BP values measured by the BP measuring device from the living body. The BP measuring apparatus outputs the BP values accumulatively stored in the BP-value storing device, each time a new BP value or values of the subject is/are measured by the BP measuring device. Thus, the living body can easily recognize the time change of his or her BP values and effectively utilize the BP values for his or her health control. However, in the case where the BP values output from the BP apparatus do not fall within a normal BP range and care should be taken of the living body, just the marshalling of figures would give only a weak visual impression to the living body. Even if the living body may recognize his or her blood pressure abnormality, he or she is likely to forget it. While it is possible to output a pictorial image together with the BP values to give a stronger visual impression to the living body, it needs much time and effort to prepare the pictorial image or images. Moreover, in the case where a doctor gives a blood pressure-treating medicine to a patient after having made a diagnosis based on measured BP values, it may be somewhat cumbersome for the doctor to explain the directions for use of the medicine, the objects of administration of the same, and other necessary items.
Next, there is known an arm belt which is, either manually or using a winding device, wound around an upper arm of a living body or subject and which has an inflatable bag to which a pressurized air is supplied to press the arteries of the arm and measure a BP value or values of the subject. The supplying of the air to the bag is effected after the belt is wound around subject's arm, and the measurement of BP values is carried out while the air pressure of the bag is changed. It is preferred that the belt be wound around the arm such that three fingers can be inserted between the skin of the arm and the inside surface of the belt. However, since the upper arm of the subject around which the arm belt is wound is easily deformable, a certain level of skill is needed for winding the belt wound the arm with a preferable pressing force and measuring a BP value or values of the subject with accuracy. Hence, there has been used a winding device which automatically winds an arm belt around an upper arm of a living subject. The automatic winding device has a cylindrical arm receiver in which the belt taking a cylindrical shape is provided, and has a drive device such as a motor for tightening the belt. After the subject inserts his or her arm into the belt inside the receiver through one end of the receiver, the drive device is operated to tighten the belt and thereby reduce the inside diameter of the cylindrical belt. Thus, the arm belt is automatically wound around the subject's upper arm. When a BP measurement is carried out using the automatic winding device, it is required that the arteries of the upper arm of the subject be uniformly pressed by the arm belt. To this end, generally, an elbow rest is provided outside the other end of the arm receiver, and the subject inserts his or her arm such that the elbow of the arm rests on the rest. The diameter of the belt is reduced when the subject is taking such a posture that the upper arm is not in contact with the inner wall of the above-mentioned one end of the receiver. That is, it is preferred that the longitudinal axis line of the upper arm of the subject be kept substantially parallel to the central axis line of the cylindrical arm receiver. However, ordering the subject to change his or her natural posture to the above-mentioned posture may result in forcing the subject to take an unnatural posture, depending upon the conformation of his or her body. This problem is exaggerated in particular for patients or aged persons who are not so free to change their postures. In the latter cases, the accuracy of BP measurements may be lowered.
There is known a BP monitor apparatus which monitors the blood pressure of a living subject. The BP monitor apparatus includes an automatic BP measuring device including an inflatable cuff adapted to be wound around a body portion of the subject. The automatic BP measuring device is iteratively started to measure a BP value or values of the subject. Thus, the BP monitor apparatus carries out BP measurements periodically, i.e., at a prescribed measurement period. However, if the measurement period is prescribed at so short a period to improve the reliability of the BP monitoring, the frequency of pressing of the subject's body portion with the cuff is increased so that the subject feels a heavy burden. In this situation, there has been proposed a BP monitor apparatus which increases the pressure of an inflatable cuff wound around a body portion of a living subject, up to a prescribed target pressure value, detects a pulse wave as a pressure oscillation produced in the cuff, and continuously estimates a BP value or values based on a magnitude or magnitudes of each of successive heartbeat-synchronous pulses of the pulse wave. Examples of this BP monitor apparatus are disclosed in Non-Examined Japanese Patent Applications No. 61(1986)-103432 and No. 60(1985)-241422. In the latter case, however, if the target pressure is prescribed at as low as possible a value to reduce the burden to the subject, it might be difficult to detect the change of respective amplitudes of successive pulses of the pulse wave corresponding to the change of BP values of the subject. That is, the reliability of the BP monitoring is lowered. The pulse amplitudes detected from the cuff set on people having normal blood pressure change with the cuff pressure so as to have an envelope indicated at solid line in FIG. 29, whereas the pulse amplitudes obtained from people having low blood pressure change with the cuff pressure so as to have an envelope indicated at broken line. Since the amount of change of the pulse amplitudes with respect to the amount of change of the BP values of a subject is more or less small where the pulse amplitudes are obtained at a relatively low cuff pressure such as a value, P.sub.K, shown in FIG. 29, the reliability of the BP monitoring at the low cuff pressure P.sub.K is insufficiently low.
Furthermore, there is known an automatic BP measuring apparatus which quickly increases the pressure of an inflatable cuff wound around a body portion of a living subject, up to a target pressure value at which the inflated cuff stops the blood flow through the arteries of the body portion, subsequently slowly decreases the cuff pressure at a rate of 2 to 3 mmHg/sec, and measures a BP value or values of the subject during the slow decreasing of the cuff pressure. There are known two BP measuring techniques, i.e., oscillometric method and Korotkoff-sound method. In the oscillometric method, the pressure oscillation produced in the cuff during the slow decreasing of the cuff pressure is detected as a pulse wave, and the systolic and diastolic BP values of the subject are determined based on the change of respective amplitudes of successive heartbeat-synchronous pulses of the pulse wave. In the Korotkoff-sound method, the Korotkoff sounds, i.e., blood-flow sounds produced from the arteries of the body portion during the slow decreasing of the cuff pressure are detected using a microphone, and the systolic and diastolic BP values of the subject are determined based on the two cuff-pressure values at which the first and last Korotkoff sounds are detected, respectively. In these BP measuring methods, the accuracy of measurement of BP values depends on the amount of change of the cuff pressure corresponding to the interval of occurrence of the successive pulses of the pulse wave or the successive Korotkoff sounds. Therefore, for measuring the BP value or values of the subject with accuracy, the automatic BP measuring apparatus carries out the BP measurement while the cuff pressure is slowly decreased. However, since in the prior BP measuring apparatus the cuff pressure is slowly decreased in carrying out the BP measurement, it takes about twenty seconds to obtain the measured BP value or values of the subject. Before this slow cuff-pressure decreasing, no BP value is available to a medical worker such as a doctor. In the case where a doctor should make a quick decision on an emergency patient, or in the case where a target value higher by a prescribed value than the systolic BP value of a subject should be determined while the cuff pressure is quickly increased, so that the cuff pressure is stopped at the thus determined target value, it is required that a BP value of the subject be known, even though it is rough, before a BP measurement is carried out during the slow decreasing of the cuff pressure.
Moreover, there is known the oscillometric BP measuring method in which heartbeat-synchronous signal waves generated from arteries of a living subject are collected while the pressure of an inflatable cuff applied to the arteries is changed, the respective amplitudes of the signal waves are determined to provide a series of wave amplitudes arranged in the order of generation of the signal waves, and a BP value of the subject is determined based on a change of the series of wave amplitudes according to a prescribed software algorithm. An example of the BP measuring method is disclosed in Examined Japanese Patent Application laid open for opposition under Publication No. 2(1990)-25610 assigned to the Assignee of the present U.S. application. The Japanese document discloses a BP measuring apparatus which measures a BP value of a living subject according to the oscillometric BP measuring method, i.e., prescribed software algorithm. The BP measuring apparatus has a display device which displays a series of wave amplitudes in a two-dimensional graph having a first axis indicative of the cuff pressure and a second axis indicative of the wave amplitude. A medical worker such as a doctor can easily recognize, from the distribution of the wave amplitudes with respect to the cuff pressure, the amounts of error of the BP measurement due to external causes such as the physical motion of the subject and the noise produced from peripheral devices. Thus, the doctor can judge whether the conditions of the BP measurement are proper or appropriate. A series of wave amplitudes displayed in the two-dimensional area provided on the display device may define a complex envelope changeable depending upon external factors. There have been employed various smoothening techniques each of which is used to smoothen the envelope of the wave amplitudes obtained in carrying out a BP measurement. The BP measuring method disclosed in Non-Examined Japanese Patent Application laid open for inspection under Publication No. 63(1988)-51837 is one of the smoothening techniques. In this method, an odd number of successive amplitudes are selected from the series of amplitudes, and the amplitude positioned at the center of the selected amplitudes is replaced with the amplitude having the median magnitude. This is the so-called medical filter. By sequentially repeating this median-filter treatment with all the amplitudes by removing the oldest one of the odd number of amplitudes and adding the following amplitude, the envelope of the amplitudes is smoothened. Since a BP measurement is carried out based on the thus smoothened envelope of the amplitudes, the accuracy of measurement of BP values is increased. Although a series of amplitudes are displayed as a two-dimensional graph on the display device, the amplitudes defines only a smoothened envelope wherein the errors of amplitudes due to external factors have been corrected. From a smoothened envelope, a doctor cannot judge whether the conditions of measurement of BP values are proper, unlike a non-smoothened envelope showing the distribution of non-treated "raw" amplitudes from which the doctor can judge.